multi-project build example: 2 common libraries, and 3 application projects. All projects are java.

build.scala

import sbt._
import sbt.Keys._
import android.Keys._

object ExampleMultiBuild extends Build {
  // define a new task
  val release = TaskKey[Unit]("release", "build & release all release builds")

  // setup an aggregate for 'install' and 'release'
  // calling either will perform the install or release operation against
  // all 3 applications
  lazy val root = Project(id = "top", base = file(".")) settings(
    android.Plugin.androidCommands :+
    (install <<= ( // install all apps
		install in (foo, Android),
		install in (baz, Android),
		install in (bar, Android)) map { (_,_,_) => () }) :+
          (release <<= (
                packageRelease in (foo, Android),
                packageRelease in (baz, Android),
                packageRelease in (bar, Android)) map { (_,_,_) => () }): _*
  ) aggregate(core, common, foo, baz, bar)

  // define a core library
  lazy val core = Project(
    id = "corelib", base = file("CoreLibrary")) settings(
      android.Plugin.androidBuild: _*)

  // define a common library
  lazy val common = Project(
    id = "commonlib", base = file("CommonLibrary")) settings(
      commonlibSettings: _*) dependsOn(core)

  // define the 3 end-application projects
  lazy val foo = Project(
    id = "foo-app", base = file("FooProject")) settings(commonSettings: _*) dependsOn(common)
  lazy val bar = Project(
    id = "bar", base = file("BarProject")) settings(commonSettings: _*) dependsOn(common)
  lazy val baz = Project(
    id = "baz", base = file("BazProject")) settings(commonSettings: _*) dependsOn(common)

  // declare settings for commonlib
  // 'watchSources' is modified so that .swp files don't cause resources
  // to rebuild while viewing with vim (but not saving)
  lazy val commonlibSettings = android.Plugin.androidBuild(core) ++ Seq(
    watchSources ~= { _.filterNot(_.isDirectory) },
    javacOptions += "-Xlint:deprecation")

  // declare common settings for the foo, bar and baz projects
  // notice the use of androidBuild(core, common) to define the
  // compile dependency on those projects
  lazy val commonSettings = android.Plugin.androidBuild(core, common) ++ Seq(
    run <<= run in Android,
    javacOptions += "-Xlint:deprecation")
}